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SWAPCTL(8)                  System Manager's Manual                 SWAPCTL(8)

     swapctl, swapon - system swap management tool

     swapctl -A [-f | -o] [-n] [-p priority] [-t blk|noblk|auto]
     swapctl -D dumpdev|none
     swapctl -U [-n] [-t blk|noblk|auto]
     swapctl -a [-p priority] path
     swapctl -c -p priority path
     swapctl -d path
     swapctl -l | -s [-k | -m | -g | -h]
     swapctl -q
     swapctl -z
     swapon -a [-t blk|noblk]
     swapon path

     The swapctl program adds, removes, lists, and prioritizes swap devices
     and files for the system.  The swapon program acts the same as the
     swapctl program as if called with the -a option, except if swapon itself
     is called with -a in which case swapon acts as swapctl with the -A

     The following options are available:

     -A      This option causes swapctl to read the /etc/fstab file for
             devices and files with a "sw" or "dp" type, and adds all "sw"
             type entries as swap devices and sets the last "dp" type entry as
             the dump device.  If no swap devices are configured, swapctl will
             exit with an error code.  If used together with -t auto this
             option will not read /etc/fstab but query the kernel for all swap
             partitions on local hard disks.

     -a      The -a option requires that a path also be in the argument list.
             The path is added to the kernel's list of swap devices using the
             swapctl(2) system call.  When using the swapon form of this
             command, the -a option is treated the same as the -A option, for
             backwards compatibility.

     -c      The -c option changes the priority of the listed swap device or

     -D      The -D option requires that a dumpdev also be in the argument
             list.  The kernel dump device is set to dumpdev.  The word "none"
             can be used instead of a dumpdev to disable the currently set
             dump device.  This change is made via the swapctl(2) system call.
             The dump device is used when the system crashes to write a
             current snapshot of real memory, to be saved later with
             savecore(8) at system reboot, and analyzed to determine the

     -d      The -d option removes the listed path from the kernel's list of
             swap devices or files.

     -f      Used in combination with the -A command and -t auto flag this
             option makes swapctl use the first discovered swap device to also
             become the dump device.  The -f option is mutually exclusive with
             the -o option.

     -g      The -g option uses (1024 * 1024 * 1024) byte blocks instead of
             the default 512 byte.

     -h      The -h option uses humanize_number(3) to display the sizes.

     -k      The -k option uses 1024 byte blocks instead of the default 512

     -l      The -l option lists the current swap devices and files, and their
             usage statistics.

     -m      The -m option uses (1024 * 1024) byte blocks instead of the
             default 512 byte.

     -n      Used with the -A or -U command, the -n option makes swapctl print
             the action it would take, but not actually change any swap or
             dump devices.

     -o      Similar to the -f flag, this "Dump Only" option makes swapctl
             find the first swap device and configure it as dump device.  No
             swap device is changed.  This option needs to be used in
             combination with -A -t auto and is mutually exclusive with -f.

     -p      The -p option sets the priority of swap devices or files to the
             priority argument.  This works with the -a, -c, and -l options.

     -q      Query /etc/fstab, checking for any defined swap or dump devices.
             If any are found, swapctl returns with an exit status of 0, if
             none are found the exit status will be 1.

     -s      The -s option displays a single line summary of current swap

     -t      This flag modifies the function of the -A and -U options.  The -t
             option allows the type of device to add to be specified.  An
             argument of blk causes all block devices in /etc/fstab to be
             added.  An argument of noblk causes all non-block devices in
             /etc/fstab to be added.  An argument of auto causes all swap
             partitions on local hard disks to be used.  This option is useful
             in early system startup, where swapping may be needed before all
             file systems are available, such as during disk checks of large
             file systems.

     -U      This option causes swapctl to read the /etc/fstab file for
             devices and files with a "sw" type, and remove all these entries
             as swap devices.  If no swap devices are unconfigured, swapctl
             will exit with an error code.  If used together with -t auto this
             option will not read /etc/fstab but unconfigure all local swap

     -z      The -z option displays the current dump device.

     The NetBSD swap system allows different swap devices and files to be
     assigned different priorities, to allow the faster resources to be used
     first.  Swap devices at the same priority are used in a round-robin
     fashion until there is no more space available at this priority, when the
     next priority level will be used.  The default priority is 0, the
     highest.  This value can be any valid integer, with higher values
     receiving less priority.

     When parsing the /etc/fstab file for swap devices, the following options
     are recognized:

     priority=N      This option sets the priority of the specified swap
                     device to N.
     nfsmntpt=/path  This option is useful for swapping to NFS files.  It
                     specifies the local mount point to mount an NFS
                     filesystem.  The mount point must exist as a directory.
                     Typically, once this mount has succeeded, the file to be
                     used for swapping on will be available under this point
                     mount.  For example:

                     server:/export/swap/client none swap sw,nfsmntpt=/swap

     If the requested operation was successful, the swapctl utility exits with
     status 0.  If an error occurred, the exit status is 1.

     The -A and -U operations (add or remove swap devices listed in fstab(5))
     return an exit status of 2 to report that no suitable swap devices were

     The -z operation (query dump device) and -l (list swap partitions) return
     an exit status of 1 if no dump device or swap partition has been
     configured.  If any swap partition is available or a dump device is set,
     the respective query returns 0.

     swapctl(2), fstab(5), mount_nfs(8)

     The swapctl program was first made available in NetBSD 1.3.  The original
     swapon program, provided for backwards compatibility, appeared in 4.0BSD.

     The swapctl program was written by Matthew R. Green <mrg@eterna.com.au>.

     Using the automatic swap partition detection done by the -A -t auto
     option may be dangereous.  Depending on the on-disk partitioning scheme
     used, the type of a partition may not be accurately recognizable as a
     swap partition.  The autodetection might recognize and use partitions on
     removable media like USB sticks.  An easy way to test the
     autoconfiguration is to use swapctl with the -n option.

     If no swap information is specified in /etc/fstab, the system startup
     scripts (see rc(8)) will configure no swap space and your machine will
     behave very badly if (more likely when) it runs out of real memory.

     Local and remote swap files cannot be configured until after the file
     systems they reside on are mounted read/write.  The system startup
     scripts need to fsck(8) all local file systems before this can happen.
     This process requires substantial amounts of memory on some systems.  If
     you configure no local block swap devices on a machine that has local
     file systems to check and rely only on swap files, the machine will have
     no swap space at all during system fsck(8) and may run out of real
     memory, causing fsck to abnormally exit and startup scripts to fail.

NetBSD 10.99                     June 1, 2011                     NetBSD 10.99